A burn can be an injury caused by heat, cold, electricity, chemicals, or radiation. Burns usually affect the skin, although other important areas of the body can also be injured. The severity of a burn of the skin depends on how deeply it has affected the tissue. There are three categories of burn: superficial, partial thickness and full thickness. These were previously referred to as first, second and third-degree burns.
Superficial burn is a burn that only affects epidermis, the surface of the skin. The skin appears red (erythema) and slightly swollen, and the burn is almost always painful. Partial thickness burn is a deeper burn, but it does not affect the whole depth of the skin. The epidermis is destroyed and the dermis, which is the layer of skin tissue below the epidermis, is also damaged to varying degrees. The skin appears deep red or purple, swollen and blistered, and the surface may have a weeping, wet appearance. The skin is extremely painful and hypersensitive, even to air movement. In the case of full thickness burn, the full depth of the skin is damaged and the skin appears dry and leathery. The skin may be pale or blackened. The full thickness burns are painless, because the nerve endings within the skin are also destroyed, although there is usually pain in the surrounding areas if they are affected by partial thickness burns.
Scalding is a specific type of burning that is caused by hot fluids (i.e. liquids or gases). Examples of common liquids that cause scalds are water and cooking oil. Steam is a common gas that causes scalds. Young children, with their delicate skin, can suffer a serious burn in a much shorter time of exposure than the average adult.
Sunburn is a burn to living tissue such as skin produced by overexposure to ultraviolet (UV) radiation. Sunburn of the skin occurs when incident UV radiation exceeds the existing protective capacity of melanin in the skin. A similar burn can be produced by overexposure to other sources of UV such as from tanning lamps, or occupationally, such as from welding arcs. Typically there is initial erythema, followed by varying degrees of pain, both proportional in severity to the duration and intensity of exposure. Other symptoms are edema, itching, red and/or peeling skin and rash. Sunburns may be superficial or partial thickness burns, or first- or second-degree burns.
In the recent years, another commonly seen burn caused by radiation is the burn caused by laser radiation used in laser therapy for cosmetic facial treatments and hair removal procedures. Laser facial resurfacing has been used to remove the upper layers of the skin on the face and it is an effective treatment for reducing mild scarring, or the effects of sun damage, such as fine wrinkles. In laser facial resurfacing procedure, a laser beam is radiated on the selected area of face to destroy epidermis in a carefully controlled manner, exposing the dermis. Then, at lower power, the laser heats the dermis, which stimulates the growth of new collagen fibers. Pulses of laser light can be used to treat skin lesions such as port wine stains and spider veins. These lasers can also be used to remove the color from tattoos and do not seriously damage the surrounding skin. Carbon dioxide or YAG lasers are often used for resurfacing procedures. The commonly seen side-effects of laser resurfacing include swollen skin that may ooze for the first 7-14 days after treatment and skin redness that may last for 6-12 weeks.
Laser hair removal is well established as an effective form of treatment for unwanted body hair, which is based on selective photothermolysis, or selective destruction of the follicular unit, resulting in significant hair reduction in treated areas. Adverse effects of laser hair removal are primarily related to epidermal damage by partial absorption of laser energy by the surrounding skin. This effect has been more pronounced in darker-skinned individuals whose increased skin melanin concentration places them at a higher risk of adverse effects. These adverse effects include blistering, hypo- or hyperpigmentation, scabbing, and rarely, permanent scarring.
Currently, superficial or partial thickness burns caused by heat is typically treated by flooding the affected areas with cold water until medical help, if necessary, is available. Large areas of partial thickness burns require medical treatment in hospitals, which typically involves applying dressings to protect the damaged skin. Superficial burns usually do not need dressings. Various over-the-counter ointments, creams and lotions are available for home treatment of minor burns, including sunburns. These topical compositions may include Aloe Vera, calamine, menthol, emu oil or other herbal ingredients. However, existing topical compositions have limited effects in reducing pain and preventing blistering caused by the burns. Even when they are applied immediately on the affected areas, or applied multiple times, they may not substantially reduce pains, typically they do not prevent blistering to occur.
It is known that the avermectin family of compounds is a series of very potent antiparasitic agents useful against a broad spectrum of endoparasites and ectoparasites in mammals and also having agricultural utilities against various nematode and insect parasites found in and on crops and in soil. Ivermectin is a member of the avermectin family; it has been used as an antiparasitic agent to treat various animal parasites and parasitic diseases since mid-1980's. It is commercially available for animal use as Cardomec (for felines), Zimecterin (for equines) and Ivomec (for bovines) by MERIAL Limited, Duluth, Ga. The medicine is available in tablets, paste, or chewables for heartworm prevention, topical solution for ear mite treatment, or as oral or injectable solution for other parasite problems.
Ivermectin is also commercially available from Merck & Co., Inc for human use as Stromectol® for eradication of threadworm Strongyloides stercoralis, and for eradication of Onchocerca volvulus. The medicine is available in tablets and is orally administered by the patients.
Magda et al., Amer. J. Trop. Med. Hyg. 53(6) 1995 pp. 652-653 describe a method of topical application of ivermectin to treat head lice. U.S. Pat. No. 5,952,372 (to McDaniel) discloses a method of treating a form of rosacea associated with the ectoparasite Demodex. U.S. Pat. Nos. 6,133,310, 6,433,006, 6,399,652, 6,399,651 and 6,319,945 (to Parks) disclose methods of treating acne rosacea, seborrheic dermatitis, acne vulgaris, transient acantholytic dermatitis, acne miliaris necrotica, acne varioliformis, perioral dermatitis, and acneiform eruptions by topically applying an avermectin compound, particularly ivermectin, to the affected areas.
However, avermectin compounds have not been used for treating burns caused by heat or by UV or laser radiation. It is also noted that none of the above described parasitic diseases and dermatological conditions are related to burns caused by heat or by UV or laser radiation.
Burns of the skin caused by heat, or by UV or laser radiation are common public problems. Therefore, there is a need for new and effective topical compositions for treating burns, particularly a topical composition which can be applied immediately after burning occurs to prevent blistering, and to reduce pain and other symptoms.